Favorite CISCO Study Links

(Sorry, I've still got to add in descriptions of the links dealing with 'troubleshooting,' below!)

BASIC EXAM INFORMATION

http://www.lilligren.com/cisco/daveccna.htm

Dave Lilligren, "Dave's Study Tips for CCNA™ Exam 640-607." (Tips for an outdated exam--but this is a good basic outline of many of the things you will need to know on the current exam.)

http://www.lilligren.com/cisco/daveccna_640-801.htm

Dave Lilligren, "Dave's Study Tips for CCNA™ Exam 640-801." (Information about the exam people take now!)
BASICS of NETWORKING

http://www.petri.co.il/networking.htm

http://www.informit.com/library/library.aspx?b=CCNA_Practical_Studies

From InformIT; a great explanation of routers and their memory/storage!
COMMANDS, COMMAND SUMMARY

(A "cheat sheet" -- a list of commands, and what each does)

http://www.cisco.com/en/US/docs/ios/fundamentals/command/reference/cf_book.html

(CISCO's Command Reference actually gives the commands and sample outputs! You need to learn commands and their sample outputs--you can list the commands that are in your book [if you buy the book below] and then look them up here to find the output; for more command references from CISCO see http://tools.cisco.com/search/results/en/us/get#q=command+reference+cisco+guide)
NETWORK SECURITY

http://hackathology.blogspot.com/2007/03/cisco-street-commands-pt-3_13.html

How to control user access (passwords & such)
ISDN--Dial-On-Demand CONNECTIONS

http://www.ftj.agh.edu.pl/complab/doc/Cisco_IOS_11.0/arbook/arddr.htm

A list of dial-on-demand routing commands and when to use them! (For more information on dial-on-demand see CISCO's configuration examples at http://www.cisco.com/en/US/tech/tk801/tk133/tech_configuration_examples_list.html and the Wikipedia article http://en.wikipedia.org/wiki/Dial-on_Demand_Routing
TROUBLESHOOTING SERIAL CONNECTIONS: Point-to-Point, Frame Relay

http://www.tek-tips.com/faqs.cfm?fid=1310

"Understanding the SHOW INTERFACE SERIAL stats" (Tek-Tips FAQ; Posted: 30 Nov 01; Edited 31 May 02; Retrieved Summer, 2008); this is a great summary of what different command output means! You absolutely need to get familiar with reading command output.

http://www.dummies.com/how-to/content/troubleshooting-serial-connections.html

http://www.cisco.com/en/US/docs/internetworking/troubleshooting/guide/tr1915.html#wp1020563

http://www.groupstudy.com/archives/cisco/200308/msg00888.html
CISCO Test-preparation BOOK

http://www.informit.com/store/product.aspx?isbn=9781587201820

Wendell Odom, CCENT/CCNA ICND1 Official Exam Certification Guide (CCENT Exam 640-822 and CCNA Exam 640-802), 2nd Edition.
(This book deals with what is on the test and has several good practice questions, as well as a CD to practice the exam on. There are however several corrections to this guide that are only available online; see http://www.ciscopress.com/content/images/9781587201820/Errata/1587201828_Errata.doc
My notes on Example 15-9 p. 493: the correct interfaces for example 15-9 on p. 493 were identified in my text, but if they are not in yours, they should be S 0/0/1 and S 0/1/1 respectively, as is noted in the errata.
The paste-in code specifies the new ip address for interface fa 0/1 [fast ethernet, the 0/1 port slot] as 192.168.2.23, with a net mask of 255.255.255.240. [The ip address was 192.168.4.30.] However, the fa 0/1 interface is connected to computer 23 whose ip address is 192.168.4.23 with a net mask of 255.255.255.240. You can see from the net mask [when you get to understand net masks] that it is the first three numbers of the ip address--192.168.4 in one case and 192.168.2 in another -- (along with the first four leading 0's in the binary version of the last number) make up the network or subnet portion of the address. These numbers are now different, and so specify different networks or subnets. Alas, with the new fa 0/1 address, the router interface [which was the default gateway] and computer 23 will be on different subnets! In addition, a default gateway has been specified for computer 23, and that gateway address will no longer be valid -- since the address of that interface will have been changed [that address will now not be in use]. Computer 23 will become reachable only via router 2 -- which will still have an interface on the same subnet as computer 23 -- and computer 23 will not be able to reply to any packets sent to it since its default gateway will now be misconfigured -- that is the address configured will be invalid.
And it would be pointless to try to configure the new address of the old default gateway interface as the default gateway address -- since these addresses are now on different subnets, and default gateways of course must be on the same subnet!
But you don't want to simply change the 2 in the third position of the new fa 0/1 interface to a 4 so that it and computer 23 are again on the same subnet; that is you don't want to reconfigure the address for fa 0/1 as 192.168.4.23 either.)

(Summer, 2008; posted by CEW; last updated May, 2009)